This invention relates to a lubricating oil supply unit for machines and particularly a system for lubricating two-cycle internal combustion engines.
The necessity for lubricating mechanisms having moving parts is well known. Various types of lubricating systems have been proposed including both closed systems in which the lubricant is recirculated and so-called open systems wherein the lubricant is supplied to the mechanism and dissipated to the atmosphere during the mechanism operation. Although the latter type of system has the advantage of simplicity, the discharge of lubricant to the atmosphere can cause obvious problems.
Internal combustion engines are a specific example of mechanisms which require lubrication. Generally four-cycle engines are lubricated by closed systems while two-cycle engines, because of their very nature, are lubricated by open systems. Although it was previously the practice to lubricate a two-cycle engine by mixing lubricant with the which it consumed, these lubrication methods are not at all satisfactory because they provide the same amount of lubricant under widely varying running conditions while the actual engine requirements are different. In addition, they tend to provide excess lubricant so that the most severe conditions will be met and thus there is a large amount of lubricant consumed and discharged to the atmosphere.
Systems have been proposed for providing direct delivery of lubricant to the engine and the measuring of the amount of lubricant required and supplying only that amount of lubricant required for a given running condition. Conventionally these systems have employed lubricant pumps that are driven by the engine with the amount of lubricant varied by either changing the delivery intervals for the lubricant or by changing the amount of lubricant pumped by the pump during each cycle. Although these systems offer more accurate control of the amount of lubricant than when it is mixed with the fuel, they still have some disadvantages.
For example, if the delivery interval is changed in order to control the amount of lubricant delivered to the engine, the effect of internal leakage within the pump itself cannot be ignored. That is, the amount of lubricant actually pumped is not that which is the theoretical capacity of the pump. For example, with a piston-type pump, the piston displaces a certain volume of, fluid during each pumping cycle but the volume of fluid that is actually delivered is not equaled to the displacement volume of the piston during its stroke due to internal leakage. Of course, the amount of leakage will vary with the pump operation and thus it is somewhat difficult to ensure accurate amount of lubricant delivery with this type of system. These problems are particularly acute when the system is providing lubricant for a fairly long delivery period since the amount of internal leakage will obviously increase and hence the actual amount of oil supplied decreases as does the accuracy of the oil supply.
If the pump stroke is varied in response to engine conditions, then a complicated feedback system is required and the mechanism for controlling the amount of lubricant delivered per stroke of the pump becomes complicated and costly.
It is, therefore, a principal object of this invention to provide an improved lubricant delivery system for a machine wherein the amount of lubricant delivered can be accurately controlled and internal pumping losses minimized.
It is a further object of this invention to provide an , improved method and apparatus for controlling the supply of lubricant to a two-cycle internal combustion engine. It has been determined in accordance with this invention that the amount of lubricant supplied to an engine can be more accurately controlled if the lubricant supply incorporates a pumping device that pumps a finite amount of lubricant during a single cycle of its operation. This lubricant pump is then driven by a drive that is operated incrementally with the increments being chosen to satisfy the instantaneous lubricant requirements of the engine. Once the requisite number of increments have been met, then the lubricant pump will deliver a finite amount of lubricant. With such an arrangement, the internal leakage of the pump will be constant under all conditions and hence this internal leakage will not adversely effect the accuracy of the lubricant amount.
With such a type of lubricant system, the use of complicated feedback controls can be avoided. However, it is also desirable to insure that the actuate position of the pump during its cycle is accurately monitored so as to avoid possible errors.
It is, therefore, a still further object of the invention to provide a lubrication supply system of this type and further including means for monitoring the condition of the pump and altering its operation in the event discrepancies are encountered.
With this type of lubricating system, the drive for the pump conveniently can employ an electrical stepping motor. However, the output of such stepping motors can vary in response to the electrical power applied to it. Therefore, it is a still further object of this invention to provide an improved electrical stepping motor that can be operated so as to provide equal increments of movement regardless of the voltage available to drive the stepping motor.
In conjunction with stepping motors, it is obviously desirable to reduce the amount of power consumed so as to reduce the possible discrepancies in pump output or pump condition due to variations in voltage. It is, therefore, a still further object of this invention to provide an improved type of stepping motor wherein power consumption is reduced.
With the use of stepping motors, conditions may occur that the motor will become heated and this can effect the operation of the motor and also the amount of lubricant supplied by the lubricant pump that is driven by the stepping motor. It is, therefore, a still further object of this invention to provide an improved arrangement and stepping motor where in the drive for the stepping motor is such that the temperature is maintained at a low level.
The low power consumption and temperatures are particularly important with using stepping motors. In conventional applications for stepping motors, the stepping motor does not operate over long time intervals, but rather only operates to achieve small adjustments under most circumstances. However, when a stepping motor is used for driving a lubricant supply, then it is driven much more frequently than with conventional operations and the maintenance of low power consumptions and low temperatures are particularly important.
It is, therefore, a still further object of this invention to provide an improved stepping motor that can be on a relatively continuous basis and yet with low power consumptions and at low heat generation.